JP6517612B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire.

  The contact surface of the tire is a curved surface that protrudes outward in the tire radial direction toward the center in the tire width direction. Therefore, the contact surface of the shoulder land portion on the outer side in the tire width direction has a shorter length in the tire circumferential direction than the contact surface on the inner side of the land portion in the tire width direction. Therefore, the contact pressure applied to the shoulder land portion is high, which is an obstacle to the improvement of the braking performance.

  Therefore, as a countermeasure, lowering the contact pressure applied to the shoulder land portion can be mentioned by increasing the contact area of the shoulder land portion. As a method of increasing the contact area of the shoulder land portion, for example, as described in Patent Document 1, a method in which the entire shoulder land portion of the tread rubber is projected outward in the tire radial direction than the profile line of the center region can be considered. When the entire shoulder land portion protrudes outward in the tire radial direction, the contact surface of the tread rubber becomes longer in the tire circumferential direction and the tire width direction, and the contact area increases.

JP, 2006-168638, A

  However, when the entire shoulder land portion protrudes outward in the tire radial direction, rolling resistance of the tire is deteriorated due to an increase in the amount of tread rubber used for the tire, and fuel efficiency is deteriorated.

  This invention is made in view of such a situation, and makes it a subject to provide the pneumatic tire which rolling resistance and braking performance make compatible.

The pneumatic tire according to the embodiment is a pneumatic tire in which at least shoulder land portions on both sides in the tire width direction and land portions on the inner side in the tire width direction are formed, the tire width in the shoulder land portion and the shoulder land portion in the position in the tire width direction outer side than the end portion of the inward, the thickness of the tread rubber, Ri a thicker than average thickness of the tread rubber in the land portion of the tire width direction inner side, one or more tread rubber in the tire radial direction inner side 2 The above belt is provided, and the length in the tire width direction from the end of the shortest belt in the tire width direction to the thickest position of the tread rubber in the shoulder land portion is the shortest in the tire width direction 20% or more and 60% or less of the length in the tire width direction from the end of the belt to the end in the tire width direction on the shoulder land portion, The thickest position of the tread rubber in Ruda land portion, characterized in that in the tire width direction inner side than the end portion of the shortest belt in the tire width direction.

  In the pneumatic tire of the present embodiment, the rolling resistance and the braking performance are compatible.

BRIEF DESCRIPTION OF THE DRAWINGS The half cross section of the tire width direction of the pneumatic tire 10 of embodiment.

  FIG. 1 is a half sectional view of the pneumatic tire 10 of the present embodiment in the tire width direction. The structure of the pneumatic tire 10 of the present embodiment is symmetrical with respect to the center line CL in the tire width direction.

  The pneumatic tire 10 of the present embodiment includes a bead portion including a bead core 11 in which a bundled steel wire is coated with a rubber, and a rubber bead filler 12 provided on the outer side of the bead core 11 in the tire radial direction. Have on both sides in the width direction. The carcass 13 wraps the bead portions on both sides in the tire width direction, and forms a skeleton of the pneumatic tire 10 between the bead portions. Although two carcasss 13 are provided in the present embodiment, there may be a case where only one carcass 13 is provided.

  A plurality of members are provided on the radially outer side of the carcass 13 in the tire radial direction. Specifically, one or more belts are provided on the radially outer side of the carcass 13. The belt is a plurality of cords made of steel or the like coated with rubber. In the present embodiment, the first belt 14 on the inner side in the tire radial direction and the second belt 15 on the outer side in the tire radial direction are laminated. In the present embodiment, the second belt 15 is shorter in the tire width direction than the first belt 14. Accordingly, the end in the tire width direction of the second belt 15 is on the inner side in the tire width direction than the end in the tire width direction of the first belt 14. However, the first belt 14 on the inner side in the tire radial direction may be shorter in the tire width direction than the second belt 15 on the outer side in the tire radial direction. A belt reinforcing layer 16 is provided on the outer side in the tire radial direction of the second belt 15. The belt reinforcing layer 16 is formed by coating a plurality of cords made of organic fiber or the like with rubber. The belt reinforcing layer 16 is longer in the tire width direction than the first belt 14 and the second belt 15, and covers them from the outer side in the tire radial direction.

  A tread rubber 20 is provided on the outer side in the tire radial direction of the belt reinforcing layer 16. Further, sidewall rubbers 17 are provided on both sides of the carcass 13 in the tire width direction. The tread rubber 20 is an end S in the tire width direction of the second belt 15 which is the shorter belt of the two belts in the tire width direction (when the first belt 14 is shorter than the second belt 15 in the tire width direction It is thinner at the tire width direction outer side than the tire width direction end portion of the first belt 14, and the thinner portion overlaps the sidewall rubber 17. In the region where the tread rubber 20 and the sidewall rubber 17 overlap, either of the tread rubber 20 and the sidewall rubber 17 may be on the tire outer surface side.

  Further, an inner liner 18 is provided inside the carcass 13. In addition to the above members, a plurality of members are provided according to the functional needs of the tire.

  The tread rubber 20 is provided with a plurality of main grooves extending in the tire circumferential direction. In the case of the present embodiment, four main grooves 21 are provided. A central land portion 22 at the center in the tire width direction, a shoulder land portion 23 on both sides in the tire width direction, and a median land portion 24 between the center land portion 22 and the shoulder land portion 23 are separated by these main grooves 21. And are formed. Each of these land portions may be a rib continuing the land portion over the entire circumference of the tire, or may be divided at equal intervals by lateral grooves to form a block row.

  In these land portions, the thickness of the tread rubber 20 changes in the tire width direction. Here, the thickness refers to the thickness in the normal direction of a member (belt reinforcement layer 16 in the case of this embodiment) in contact with the tread rubber 20 inside the tread rubber 20 in the tire radial direction of the finished tire.

  Specifically, the thickness of the tread rubber 20 in the shoulder land portion 23 is thicker than the other portions of the shoulder land portion 23 at a predetermined position P in the tire width direction. Further, the thickness of the tread rubber 20 at the shoulder land portion 23 is thinner than the thickness at the predetermined position P at the end Q of the shoulder land portion 23 on the inner side in the tire width direction (the main groove 21 side) and the ground end R. ing.

  Here, the ground contact end R refers to the tire width direction end portion of the ground contact surface in a state where the pneumatic tire 10 is rim-assembled on a regular rim and has a regular internal pressure and a regular load applied thereto. Here, the normal rim is a standard rim defined in standards such as JATMA, TRA, ETRTO, etc. The normal load is the maximum load defined in the above standard. The normal internal pressure is an internal pressure corresponding to the maximum load. In general, the ground contact end R is on the inner side in the tire width direction than the tire width direction end of the belt (second belt 15 in the case of this embodiment) which is the shortest in the tire width direction. However, when the pneumatic tire 10 is used under heavy load, the ground contact end R may be outside the tire width direction end of the second belt 15 in the tire width direction.

  The thickness l of the tread rubber 20 at the predetermined position P is thicker than the average thickness m of the tread rubber 20 at the media land portion 24 next to the shoulder land portion 23. Here, the average thickness m of the tread rubber 20 in the media land portion 24 is obtained by measuring the thickness of the tread rubber 20 in the media land portion 24 at regular intervals (for example, intervals of 12 mm) in the tire width direction, and measuring the measured value It is determined on average. The thickness l of the tread rubber 20 at the predetermined position P is preferably more than 100% and 110% or less of the average thickness m of the tread rubber 20 at the media land portion 24. Further, the thickness n of the tread rubber 20 at the end portion Q on the inner side in the tire width direction of the shoulder land portion 23 is desirably equal to or less than the average thickness m of the tread rubber 20 at the media land portion 24. Furthermore, the tire width of the second belt 15 (the first belt 14 when the first belt 14 is shorter than the second belt 15 in the tire width direction), which is the shortest belt in the tire width direction, of the shoulder land portion 23 An area within a distance of less than 20% from the tire width direction end S of the second belt 15 with respect to the distance u in the tire width direction from the direction end S to the tire width direction inner end Q of the shoulder land portion 23 Regarding v, it is desirable that the thickness of the tread rubber 20 be equal to or less than the average thickness m of the tread rubber 20 in the median land portion 24.

  It is desirable that the predetermined position P, which is the position where the tread rubber 20 is thickest, be near the center in the width direction of the shoulder land portion 23. Specifically, the tire width direction end S of the second belt 15 (the first belt 14 when the first belt 14 is shorter in the tire width direction than the second belt 15) which is the shortest belt in the tire width direction Of the second belt 15 from the tire width direction end S of the second belt 15 to the tire width direction distance u from the shoulder land portion 23 to the tire width direction inner end Q Preferably, the distance is 20% or more and 60% or less.

  The way of the change of the thickness of the tread rubber 20 in the tire width direction as described above is the same at any position in the tire circumferential direction of the shoulder land portion 23.

  The thickness of the tread rubber 20 can be confirmed by the following method. First, a tire is cut parallel to the tire width direction and the tire radial direction to prepare a cut sample. If necessary, make the cut surface of the cut sample smooth by buffing or the like. Next, the bead portion of the cut sample is adjusted to the rim width of the normal rim, and the shape of the cut sample is adjusted to the shape when the tire is filled with normal internal pressure. In that state, the length from the boundary between the tread rubber 20 and the member in contact with it (the belt reinforcing layer 16 in the case of this embodiment) to the tire contact surface is the above-mentioned member (the belt reinforcing layer in the case of this embodiment) It measures in the normal direction of 16), and is taken as thickness of tread rubber 20. Here, the boundary between the tread rubber 20 and the belt reinforcing layer 16 in the cut surface of the cut sample can be represented by a curve connecting the end of the cord of the belt reinforcing layer 16 on the tire contact surface side.

  In the present embodiment, as described above, since the tread rubber 20 is thicker than the average thickness m of the tread rubber 20 at the media land portion 24 at the predetermined position P of the shoulder land portion 23, The contact surface becomes longer in the tire circumferential direction, and the contact area of the shoulder land portion 23 becomes wider accordingly. As a result, the contact pressure applied to the shoulder land portion 23 decreases, and the braking performance of the pneumatic tire 10 is improved. Moreover, as compared with the case where the entire shoulder land portion 23 protrudes outward in the tire radial direction, the rolling resistance of the tire is significantly deteriorated because the rubber amount of the tread rubber 20 used for the pneumatic tire 10 is not increased. There is no fear.

  In particular, if the thickness n of the tread rubber 20 at the inner end Q of the shoulder land portion 23 in the tire width direction is equal to or less than the average thickness m of the tread rubber 20 at the media land portion 24, it is used for the pneumatic tire 10 The amount of rubber of the tread rubber 20 to be reduced is suppressed, and there is no possibility that the rolling resistance of the tire will be significantly deteriorated.

  In addition, the length t in the tire width direction from the end S of the second belt 15, which is the shortest belt in the tire width direction, to the predetermined position P where the tread rubber 20 is thick is the shoulder land portion from the end S. If it is 20% or more and 60% or less of the length u in the tire width direction to the end portion Q on the inner side in the tire width direction of 23, the tire circumferential direction of the entire shoulder land portion 23 without causing other problems Ground contact length of the If the length t exceeds 60% of the length u, the contact length on the outer side in the tire width direction of the shoulder land portion 23 may not be sufficiently extended. When the length t is less than 20% of the length u, a portion near the end S of the second belt 15 where a difference in rigidity tends to appear on the ground contact surface is mainly in contact with the ground. There is a possibility that it may occur easily.

  If the thickness l of the tread rubber 20 at the predetermined position P is 110% or less of the average thickness m of the tread rubber 20 at the median land portion 24, the rubber of the tread rubber 20 used for the pneumatic tire 10 There is no possibility that the rolling resistance of the tire will be significantly deteriorated due to the increase in the amount.

  Various changes, substitutions, omissions, and the like can be made to the above embodiment without departing from the scope of the invention. For example, in the case where there are only two main grooves and only the center land portion and the shoulder land portion, the thickness of the tread rubber is in the center land portion on the tire width direction outer side from the tire width direction inner end of the shoulder land portion. It is sufficient if there is a position thicker than the average thickness of the tread rubber.

  The rolling resistance coefficient (RRC) and the braking performance of the tires of the comparative example and the example were evaluated. The tires of the comparative example and the example have the same structure as the pneumatic tire 10 of FIG. 1 except for the thickness of the tread rubber. That is, the tires of the comparative example and the example all have four main grooves, and have a center land portion, a media land portion, and a shoulder land portion. Moreover, as in the pneumatic tire 10 of the above embodiment, each tire has the first belt radially inward of the tire and the second belt radially outward of the tire, and the second belt is wider than the first belt in tire width. Short in the direction. The size of each tire is 205 / 60R16.

  The characteristics regarding the thickness of the tread rubber of the tire of the comparative example and the example are as shown in Table 1. In Table 1, the tread rubber thickness is represented by an index. The larger the index is, the thicker it is.

  In the tire of Comparative Example 1, the thickness of the tread rubber is the thickest at the center in the tire width direction, except for the groove portion, and gradually thinner toward the outer side in the tire width direction. The way of changing the thickness of such tread rubber is conventional. Further, in the tire of Comparative Example 2, the thickness of the tread rubber is uniform in the tire width direction except for the groove portion. The “thickness of tread rubber at a predetermined position of the shoulder land portion” in Comparative Example 1 and Comparative Example 2 in Table 1 refers to the thickness of the tread rubber at the widthwise center position of the shoulder land portion.

  On the other hand, in the tire of Examples 1 to 3, the dread rubber is the thickest at the predetermined position of the shoulder land portion as in the above embodiment. The thickness of the tread rubber at the predetermined position of the shoulder land portion is larger than the average thickness of the tread rubber at the media land portion, and the thickness of the tread rubber at the tire width direction inner end portion of the shoulder land portion becomes thinner There is. The tire width direction from the tire width direction end of the second belt to the shoulder land portion of the distance in the tire width direction (the distance corresponding to the distance t in FIG. 1) from the tire width direction end of the second belt to the predetermined position The ratio (denoted as t / u in Table 1) to the distance in the tire width direction to the inner end (the distance corresponding to the distance u in FIG. 1) is different in Examples 1 to 3 as described in Table 1.

The evaluation method is as follows.
Rolling resistance coefficient: The rolling resistance test based on JIS D4234 was implemented, the rolling resistance coefficient was calculated | required, and it indexed. The smaller the index, the smaller the rolling resistance coefficient.
Braking performance: The tire was attached to a real vehicle, and the braking distance when the traveling speed was reduced from 100 km / h to 0 km / h was measured and indexed. The larger the index, the better the braking performance.

The evaluation results are as shown in Table 1. Although the tires of Examples 1 to 3 are excellent in braking performance as compared with the conventional tire, the rolling resistance coefficient is not extremely large, and the rolling resistance and the braking performance are compatible.

DESCRIPTION OF SYMBOLS 10 ... Pneumatic tire, 11 ... Bead core, 12 ... Bead filler, 13 ... Carcass, 14 ... 1st belt, 15 ... 2nd belt, 16 ... Belt reinforcement layer, 17 ... Sidewall rubber, 18 ... Inner liner, 20 ... Tread rubber, 21 ... main groove, 22 ... center land, 23 ... shoulder land, 24 ... median land

Claims (2)

In a pneumatic tire in which at least shoulder land portions on both sides in the tire width direction and land portions on the inner side in the tire width direction are formed,
The tread rubber is thicker than the average thickness of the tread rubber in the tire width direction inner side at a position in the tire width direction outside the tire width direction inner end of the shoulder land region within the shoulder land region. Do Ri,
One or more belts are provided on the inner side in the tire radial direction from the tread rubber, and the length in the tire width direction from the end of the shortest belt in the tire width direction to the thickest position of the tread rubber in the shoulder land portion And 20% to 60% of the length in the tire width direction from the end of the shortest belt in the tire width direction to the end on the tire width direction inner side of the shoulder land portion,
The pneumatic tire wherein the thickest position of the tread rubber in the shoulder land portion is on the inner side in the tire width direction from the end of the shortest belt in the tire width direction . The pneumatic tire according to claim 1, wherein a thickness of the tread rubber at an end portion inside the tire width direction of the shoulder land portion is a thickness equal to or less than an average thickness of the tread rubber at the land portion inside the tire width direction.

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